W. L. Estes of UNC Greensboro is doing that version. I can't check
its current status, as sourceforge.net is down right now.

As far as I know Vern Paxson, the previous maintainer of 'flex',
hasn't had time to work on it since 2.5.4 came out in 1996. If you
want just bug fixes for 2.5.4 I suggest using the Debian GNU/Linux
patches, which you can get from
<http://packages.debian.org/stable/devel/flex>.